Current transformer



Aug. 2, 1932. A. o. AUSTIN CURRENT TRANSFORMER Original Filed March '7. 1950 INVENTOR Arthur 0. Austin OOOOOOOOOOOOOOOOOOO 0 '0 O0 x x x Patented Aug, 2, 1 932 UNITE STATES" muss-x ARTHUR O. AUSTIN OF N EAR BARBERTON, OHIO, ASSIGNOR, IBY MESNE ASSIGNMENTS, TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO A CORPORATION OF NEW" JERSEY This invention relates to current transformers and especially to current transform ers contained in bushing insulators, and has for one of its objects the provision of a control circuit for preventing saturation ofthe core of the transformer by flux which performs no useful purpose.

A further object of the invent on is to provide a simple and effective means for supplying energy to primary windings for the transformer. r

A further object of the invention is to provide a correction circuit for correcting varia tions in the transformation ratio and phase angle.

Other objects and advantages will appear from the following description.

The inventionis exemplified by the combination and arrangement of parts shown in the accompanying drawing and described in the following specification, and it is more particularly pointed out in the appended claims.

In the drawing:

F ig. l is a vertical sectional view of a portion of a bushing insulator showing one em bodiment of the' present invention.

Fig. 2 is a vertical sectional view of a portion of an insulator showing a modification.

' Figs. 3, 4 and 5 are diagrammatic views of other modified forms of the invention.

This application is a division of application Serial Number 433,921, filed March 7, 1930.

' In high voltage lines, it is frequently desir-able to obtain an indication of the current flowingin the high voltage conductors.

This is generally accomplished by the use of current transformers as is well known in the art. Current transformers for high voltages, however, are expensive, due to the insulation required between the primary and secondary circuits of the transformers. WVhere the current in the high tension winding is small, the

characteristics of the so-called single turn current transformers are likely to be rather poor. In the type of current transformers which utilize the insulation of high potential bushings, as shown in my prior Patent N o. l,723,000, this difficulty is largely eliminated. Instead of placing the primary wind- CURRENT TRANSFORMER Original application filed March 7, 1930, Serial No. 433,921. Divided and this application filed March 21,

1931. Serial ing of the current transformer in a gap in the main conductor formed near the central portion of the bushing, it is sometimes desirable to run leads up to the top of the bushing from the primary winding, one-of which is connected to the incoming conductor and the other of which is connected to a conductor which extends through the bushing with out interruption. This arrangement is shown in Fig. 1 in which the bushing is provided with auxiliary sleeves or baffles and 36. The incoming transmission line is connected to the reservoir 37 at the top of the bushing 10 andalead38leads down from the incoming line to the primary 39 of the current transformer. A lead 40 extends up from the op-' posite end of the primary winding and is connected to a conductor 41 which extends down through the central conductor tube 42. The conductor 41 may be in the form of an insulation covered cable and is electrically con nected to the tube 42 at its upper end as shown. The arrangement brings both ends of the coil 39 to the top of the bushing where they are accessible for testing or other purposes. By this arrangement it will be seen thatthe current goes down through the lead 38 and back through the lead 40 and then again down through the lead 41. A magnetic core 43 is provided within the primary winding 39 and a magnetic shell 44 provides a portion of the return circuit for the magnetic flux in the core 43. The secondary winding of the current transformer is shown at 45. In an arrangement of this kind, it is found that the current flowing through the conductor 41 sets up a circumferential flux in the core 43 which tends to saturate the iron of the core without producing any effect upon the secondary winding 45. The saturation of the core by this circumferential flux interferes with the useful flux set up by the coil 39. To overcome this effect, a jumper 46 is electrically connected with the tube 42, both above and below the core 43, and extends outside of the core so that the tube 42 and the jumper 46 forms a short-circuit turn interlinked with the core 43. It will be seen that the circumferential magnetic flux in the core 43 will be interlinked with this short-circuit turn so tube below the core.

that a current would tend to flow in this short-circuit turn opposing the circumthe central tube 42 but insulated from the tube. A primary winding 48 is wound about the core 43 and is provided with a lead 49 at its upper end, electrically connected to the.

tube 42 above the core, and with a lead at its lower end electrically connected to the With this arrangement, the coil 48- with its leads 49 and 50 forms a closed turn interlinked with the core 43 but including the turns 48 or. the primary winding. The circumferential flux set up in the core 43 by the current in the conductor 48 will tend to produce a current in the interlinked turn comprising the parts 48, 49 and 50, but in this case this current will be directed circumferentially about the core 43 so that it will in turn induce lines of force in longitudinal direction in the core 43, and these lines of force will induce a voltage in the secondary winding 45 producing the secondary current. This provides a very simple arrangement for energizing the current transformer. A Va able impedance may be introduced in series with the winding 48 to control the amount of current therein as shown in Fig. 3. This impedance may be automatically controlled by relays in the manner explained in my prior application Serial Number 433,921 if desired.

Fig. 4 shows one form of primary in which the current in the main lead is divided between several circuits. T he current of the several circuits being combined again in the lead 61 as it leaves the primary of the current transformer. In general, the current flowing in lead 62 passes through the center of the magnetic core. This sets up a tangential flux in the core which may be controlled to a large extent by the design of the magnetic path in the core, being retarded or accelerated as desired. If a conductor 63 passes outside of the core and is connected to the lead 62 at both ends, the voltage set up by the tangential flux in the core will cause current to flow in this lead. It the resistance 64 in the circuit 63 is low, the current flowing in this conductor will be approximately equal to that in 62 and will tend to neutralize the flux set up by current passing through 62. It is evident that the current in 60 and 61 may be that in either lead 62 or 63 which may be an advantage where heavy currents must be carried. If an impedance 64 is placed in series with the winding 63, the relative current in 62 and 63 may be controlled to a very large extent.

practically double y above may be used to change the relative amounts of current flowing in the different branch circuits for difierent values in 60 and 61, to control the ratio and phase angle over a wide range of current. The potential set up in the circuit formed by leads 62 and 63, which includes the magnetic circuit energized by the current in 62, may be used to magne tize the ma netic core with lines of force extending in a longitudinal direction of the core by using the potential to force a current around the winding 65. -The current in the winding 65 may be controlled by the number of turns and by a series impedance 66. Current in the winding 65 may be utilized to increase the current carrying capacity of the transformer circuit. W here a high current must be passed through the current transformer, the winding 65 may be made for a comparatively small current capacity by supplying the proper number of turns. This winding may, of course, be made up with taps or with coils, which may be arranged in series or multiple as desired. By controlling the characteristics of the impedances 64 and 66, a

large correction may be effected :tor ratio and phase angle. If desired, a further impedance 67 may be interposed in the conductor 62. In addition to controlling the effective current in the primary which affects the current in the secondary, by the design of the several imp'edances, it is possible to effect further corrections by the use of relays as previously described.

In Fig. 5 an arrangement somewhat similar to that in Fig. 4 is shown. In this arrangement, however, the main current flows through a winding 68 which magnetizes the core and in a circuit 69 which extends out side of the core. After passing through the winding 68 and lead 70, the current then passes down through the core of the magnetic circuit through lead 71. The current in this lead tends to set up a tangential flux in the core. By closing the circuit with a winding 72 so as to include the tangential flux in the circuit formed by 71 and72, it is possible to use the potential generated to force current through the magnetized winding 73. The current in the winding 73 may be regulated by an impedance 74 and used as a main magnetizing circuit or a corrective cir- V cuit as desired. An arrangement of this kind may have a particular advantage where it is desired to change the magnetizing force generated particularly by winding 68. As the leads from the winding 68 are returned by conductor 70, it is possible to make up this winding with taps or with several coils which may be arranged to provide the desired energizing force.

I claim:

1. A transformer having a core, conductors acting to set up magnetic fields in said core in different directions, and a closed circuit interlinked with thefields set upbyone of said conductors for neutralizing said field.

2. A current transformer comprising a core, a conductor extending thro'ughsaid core, a conductor winding surrounding said core and a conductor circuit interlinked with the lines of force set up in said core by said first-named conductor forneutralizing said lines of force.

3. A current transformer comprising a conductor, a magnetic core surrounding said conductor, a secondary Winding disposed outside of said magnetic core, and a conductor forming a closed circuit interlinked with the magnetic lines of force set up in said magnetic core by current in said conductor.

4. The combination with a conductor for alternating current, of a magnetic core surrounding said conductor, a primary winding having turns encircling said core, and a closed circuit interlinked with the magnetic lines of force set up in said core by current in said conductor.

5. A current transformer comprising a conductor, a magnetic core surrounding said conductor, primary coils encircling said core, and an energizing circuit for said coils interlinked with the magnetic lines of force set up in said core by current in said conductor.

6. A current transformer comprising a main conductor, a magnetic core surrounding said conductor, and a primary winding for energizing said magnetic core with lines of force extending longitudinally of said core, potential being supplied to said primary winding by the magnetic flux set up by current in said main conductor.

7 A current transformer having a magnetic core and a primary circuit in which the current is divided between a conductor passing through the magnetic core and a conductor passing outside the magnetic core, the current in the conductor outside of the core acting as an energizing circuit or as a corrective circuit to control the magnetic flux in the core.

8. A current transformer having a magnetic core and a primary circuit in which the current is divided between a conductor passing through the magnetic core and a conductor passing outside the magnetic core, the current in the conductor outside of the core acting as an energizing circuit or as a corrective circuit to control the magnetic flux in the core, and a main primary winding for magnetizing the core.

9. In combination a conductor, a magnetic core surrounding said conductor, a primary winding surrounding said magnetic core, a secondary winding surrounding said magnetic core and a closed conductor circuit having one portion thereof extending through said core and another portion disposed outside of said core and connected with the portion extendlng lator, of a magnetic core disposed within said insulator and having an opening therethrough extending in the direction of the axis of said insulator, a conductor extending through said opening and having one end thereof extending to one end of said insulator, a primary Winding disposed within said insulator and surrounding said magnetic core,

leads connected with the ends of said primary winding and extending to the end of said insulator, one of said leads being connected to' a terminal and the other of said leads being connected tothe conductor which extends through said core.

12A current transformer comprising a magnetic core,a conductor extending through said core, a primary winding surrounding said core, a tubular member of conducting material extending through said core and sur- 7 rounding said conductor, and a jumper electrically connected with said tubular member at opposite ends of said core and extending outside of said core and forming with said tubular member a closed circuit interlinked with said core.

18. A current transformer comprising a magnetic core, a conductor extending through said core and adapted to set up circumferential lines of force in said core when said conductor isenerg'ized bv an alternating current, a primary winding for said transformer surrounding said core and conductor, and a conducting member extending through said core and connected with the opposite ends of said primary winding respectively to form a closed circuit interlinked with thelines of force set up by said first-named conductor and including in said circuit said primary winding. 7

I 14. A current transformer comprising a magnetic core, a conductor extending through said core and adapted to set up circumferential lines of force in said core when energized by alternating current, a primary winding surrounding said core and conductor, a mem ber vof conducting material extending through I said core and connected with the respective ends ofsaid primary winding and forming a closed circuit interlinked with the lines of force set up by said conductor in said core, and an adjustable impedance in series with said closed circuit.

Too

15. A current transformer comprising a magnetic core, a primary winding surrounding said core, and means for energizing said primary winding comprising a conductor extending through said core and adapted when energized to set up circumferential lines of force in said core, and a conducting element extending through said core and electrically connected to the respective ends of said primary winding to form a closed electrical circuit interlinked with the lines of force set up by said conductor in said core.

16. The combination with a bushing insulator, of a current transformer disposed within said insulator and comprising a magnetic core having its axis extending in the direction of the axis of said insulator, a pri mary winding surrounding said core, a secondary winding surrounding said core, a conductor extending through said core and adapted when energized to set up circumferential lines of force in said core, and a conducting element extending through said core and connected with the respective ends of said primary winding and forming with said primary winding a closed circuit interlinked with the lines of force set up by said conductor in said core so that said closed circuit including said'primary winding is energized by said lines of force. I

17. A current transformer comprising a magnetic core a secondary winding placed about said core, said magnetic core having an air return magnetic path for energizing said secondary winding, a conductor extending through said magnetic core, and a closed conducting circuit threading the core for reducing or neutralizing useless flux in said core.

18. A current transformer comprising a core, a conductor extending through said core, a primary winding for magnetizing said core, a secondary winding disposed in the return path of the magnetic flux set up in said core by said primary winding and aconductor circuit linking the magnetic flux set up in said core by said first named conductor, and impedance in said circuit for controlling the phase angle and current ratio of the primary to the secondary windings of said transformer. V

19. A current transformer comprising a magnetic core, a primary winding surrounding said core, a conductor extending through said core in the direction of the axis of said primary winding, a secondary winding disposed in the return path of the magnetic field set up in saidcore bysaid primary winding, and means for utilizing the flux set up in said core by said conductor to control the phase angle or current ratio of the current in said secondary winding relative to the current in said primary winding 20. An insulator bushing having a conductor extending therethrough and having a current transformerrprimary winding disposed therein, a lead from each end of said winding extending to the top of said bushing insulator, said primary winding being connected by said leads in circuit with said conductor In testimony whereof I have signed my name to this specification this 20th day of March, A. D. 1931.

' ARTHUR O. AUSTIN.

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